This invention relates to an improved microprogram control system for a data-processing device. A data-processing device adopting a stored program system carries out the prescribed processing of data by repeating a series of steps comprised of reading out an instruction, decoding the instruction thus read out and executing the instruction.
These steps are divided into some fundamental microsteps. These microsteps are individually referred to as micro-instructions. A data-processing device adopting a microprogram control system executes various instructions formed of combinations of microinstructions. A series of microsteps constituting combinations of microinstructions is referred to as a microprogram. A memory supplied with said microprogram is referred to as a control memory.
With the above-mentioned microprogram control system, one word read out of the control memory is generally processed as a single microinstruction. Where, a parallel horizontal-type microinstruction system is applied in processing data, then the drawbacks arise that a microinstruction will have a larger number of bits; consequently, the bits constituting the control memory will increase in number; and the control memory will become more expensive, as data have to be processed more in parallel in a microstep.